The present invention relates to a process for producing tetrafluorobenzenemethanols represented by formula (4) 
(wherein m represents 1 or 2, n represents 0 or 1, and m+n=2) useful as an intermediate of pesticide or medicine and a process for producing an intermediate in the production of the tetrafluorobenzenemethanols.
More specifically, the present invention relates to a process for producing tetrafluorobenzenemethanols, tetrafluorobenzenecarbaldehyde dialkylacetals and tetrafluorobenzenecarbaldehydes which are useful as intermediates in the production of cyclopropanecarboxylic acid esters having excellent insecticidal action by a series of reactions using tetrafluorocyanobenzene as a starting material, and also relates to a novel tetrafluorobenzenecarbaldehyde dimethylacetal.
It is known that 2,2-dimethyl-3-halogenovinyl-cyclopropanecarboxylic acid esters of a benzyl alcohol substituted by from 1 to 4 fluorines and from 0 to 2 chlorines have good insecticidal action (see, German Patent Publication (OLS) No. 2,658,074). In particular, it is known that cyclopropanecarboxylic acid esters of 2,3,5,6-tetrafluorobenzyl alcohol are an excellent insecticide because these have good insecticidal action but at the same time, are low in the toxicity to mammals as compared with cyclopropanecarboxylic acid esters of pentafluorobenzyl alcohol (see, German Patent Publication (OLS) No. 3,705,224).
With respect to the process for producing tetrafluorobenzenemethanol represented by formula (4), a method of reducing a halogen-substituted benzoic acid derivative by a metal hydride such as NaBH4 and LiAlH4 has been proposed.
For example, German Patent Publication (OLS) No. 3,714,602 discloses a method where 2,3,5,6-tetrafluorobenzoic acid is reacted with NaBH4 and then treated with an alkylating agent to produce 2,3,5,6-tetrafluorobenzyl alcohol. German Patent Publication (OLS) Nos. 2,658,074, 2,714,042 and 2,661,074 disclose a method of reducing polyfluorobenzoyl fluoride by NaBH4 to produce polyfluorobenzyl alcohol and a method of reducing polyfluorobenzoyl fluoride by LiAlH4 to produce polyfluorobenzyl alcohol in which one or more fluorine substituent is defluorinated.
In British (Unexamined) Patent Publication No. 2,127,013, 2,3,5,6-tetrafluoroterephthaloyl chloride and NaBH4 are reacted to produce 2,3,5,6-tetrafluorobenzenedimethanol.
Furthermore, in European (Unexamined) Patent Publication No. 31,199, 1,2,4,5-tetrafluorobenzene and n-butyl lithium are reacted, carbon dioxide is subsequently allowed to act thereon, thereby forming 2,3,5,6-tetrafluorobenzoic acid, and this is reduced by LiAlH4 to produce 2,3,5,6-tetrafluorobenzyl alcohol.
These methods all use an expensive hydrogenated metal reagent in a stoichiometric amount and cannot be an industrially advantageous method.
In addition, for producing tetrafluorobenzenemethanol represented by formula (4), a method using an electrolytic reduction has also been proposed. For example, in JP-A-1-119686 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), pentafluorobenzoic acid is electrolytically reduced using a solid metal or solid alloy for the cathode and an aqueous solution of sulfuric acid, hydrochloric acid, phosphoric acid or sulfonic acid for the electrolytic solution, thereby producing 2,3,5,6-tetrafluorobenzyl alcohol together with 2,3,5,6-tetrafluorobenzaldehyde.
In JP-A-63-206491, a pentafluorobenzoic acid is electrolytically reduced using a solid metal or solid alloy for the cathode and a sulfuric acid aqueous solution for the electrolytic solution, thereby producing 2,3,5,6-tetrafluorobenzyl alcohol as a mixture with pentafluorobenzyl alcohol.
There have been proposed many other methods using electrolytic reduction, however, similarly to the above-described cases, a benzyl alcohol is produced as a mixture in all methods (see, J. Electroanal. Chem., page 215 (1991), J. Electroanal. Chem., page 315 (1987), J. Chem. Soc. Perkin Trans I, page 189 (1972), J. Appl. Electrochem., page 1082 (1992), and Denki Kagaku Oyobi Kogyo Butsuri Kagaku (Electrochemistry and Industrial Physical Chemistry), page 83 (1990)).
In any of these methods, the yield is low and the purity of the product is not high. Particularly, pentafluorobenzyl alcohol from which cyclopropanecarboxylic acid ester harmful to human body is derived, cannot be prevented from mixing into the product.
In order to overcome these problems, International Patent Publication No. 9808795 has proposed a process for producing a fluorinated benzyl alcohol, where fluorinated dicyanobenzene is hydrogenolized in the presence of a catalyst, the cyano group only on one side is hydrodecyanated to produce fluorinated benzonitrile, and then the cyano group of the fluorinated benzonitrile is converted into a hydroxymethyl group. In this method, the conversion of cyano group into hydroxymethyl group is attained by a method of reducing the cyano group into an aldehyde group and reducing it into a hydroxymethyl group, a method of reducing the cyano group directly into a hydroxymethyl group, or a method of hydrolyzing the cyano group into a carboxyl group and then reducing the carboxyl group into a hydroxymethyl group.
However, some problems are present in the process of converting the cyano group into a hydroxymethyl group. To speak more specifically, in the method of hydrolyzing the cyano group into a carboxyl group and then reducing the carboxyl group into a hydroxymethyl group, an expensive hydrogenated metal reagent is used in a stoichiometric amount and therefore, this is not an industrially advantageous method. In the method of reducing the cyano group directly into a hydroxymethyl group, the reaction yield is generally low. And, in the method of reducing the cyano group into an aldehyde group and then reducing it into a hydroxymethyl group, 2,3,5,6-tetrafluorobenzyl alcohol is by-produced in the process of reducing the cyano group into an aldehyde group.
The 2,3,5,6-tetrafluorobenzyl alcohol is an objective component but remains in the distillation still at the purification of aldehyde by distillation because it has a high boiling point. Therefore, this side production of 2,3,5,6-tetrafluorobenzyl alcohol causes reduction in the yield. If the 2,3,5,6-tetrafluorobenzyl alcohol having a high boiling point is recovered by distillation together with aldehyde, impurities are mixed and the product is disadvantageously reduced in the purity.
Aldehyde is an intermediate product in the successive reaction for reducing the cyano group into hydroxymethyl group, accordingly, it is very difficult to suppress the generation of benzyl alcohol as a product due to the excessive reaction. In other words, in order to maximize the yield of aldehyde, the end point of reaction must be very strictly controlled. Furthermore, in any method, a reaction solvent, a co-catalyst such as carboxylic acid, and water are used each in a large amount, and this causes problems such as bad productivity, loss of solvent or the like, and increase in the load for recovery.
Therefore, the object of the present invention is to provide industrially useful methods for manufacturing, in a high purity and a high yield, tetrafluorobenzenemethanols represented by formula (4) useful as an intermediate of pesticide or medicine and tetrafluorobenzenecarbaldehyde dialkylacetals and tetrafluorobenzenecarbaldehydes which are an intermediate in the production of the tetrafluorobenzenemethanols.
In particular, the object of the present invention is to provide a process for producing 2,3,5,6-tetrafluorobenzyl alcohol, 2,3,5,6-tetrafluorobenzaldehyde, 2,3,5,6-tetrafluorobenzenedimethanol, 2,3,5,6-tetrafluoroterephthalaldehyde, 2,3,5,6-tetrafluorobenzaldehyde dimethylacetal and 2,3,5,6-tetrafluoroterephthalaldehyde dimethylacetal, which are useful as an intermediate in the production of pyrethroids having good insecticidal action and low toxicity to human body, by an industrially advantageous method.
The present invention relates to a process for producing tetrafluorobenzenemethanols represented by formula (4), tetrafluorobenzenecarbaldehyde dialkylacetals represented by formula (2) and tetrafluorobenzenecarbaldehydes represented by formula (3) described in below (1) to (14), which are useful as an intermediate in the production of cyclopropanecarboxylic acid esters having excellent insecticidal action, by a series of reactions using tetrafluorocyanobenzene represented by formula (1) as a material. The present invention also relates to a novel tetrafluorobenzenecarbaldehyde dimethylacetal represented by formula (5).
(1) A process for producing a tetrafluorobenzenemethanol, comprising catalytically reducing a tetrafluorocyanobenzene represented by formula (1): 
(wherein m represents 1 or 2, n represents 0 or 1, and m+n=2) in the presence of an alkyl alcohol represented by Rxe2x80x94OH (wherein R represents an alkyl group having from 1 to 4 carbon atoms) and an acid to prepare a tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2): 
(wherein m and n have the same meanings as defined above), hydrolyzing it to prepare a tetrafluorobenzenecarbaldehyde represented by formula (3): 
(wherein m and n have the same meanings as defined above), and reducing it to produce a tetrafluorobenzenemethanol represented by formula (4): 
(wherein m and n have the same meanings as defined above).
(2) A process for producing a tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2); 
(wherein m and n have the same meanings as in above (1)) comprising catalytically reducing a tetrafluorocyanobenzene represented by formula (1) 
in the presence of an alkyl alcohol represented by Rxe2x80x94OH (wherein R has the same meanings as defined in above (1)) and an acid.
(3) The process for producing a tetrafluorobenzenecarbaldehyde dialkylacetal as described in above 2, wherein the alkyl alcohol is methanol and the compound represented by formula (2) is tetrafluorobenzenecarbaldehyde dimethylacetal.
(4) The process for producing a tetrafluorobenzenecarbaldehyde dialkylacetal as described in above (2) or (3), wherein the catalyst used in the catalytic reduction is sponge nickel.
(5) The process for producing a tetrafluorobenzenecarbaldehyde dialkylacetal as described in any one of above (2) to (4), wherein copper, tin or zinc as a dissimilar metal component is added to the catalyst used in the catalytic reduction.
(6) The process for producing a tetrafluorobenzenecarbaldehyde dialkylacetal as described in any of above (2) to (5), wherein the catalytic reduction is carried out under condition that the amount of water present in the reaction is 1 time in mol or less based on the acetal group of tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2).
(7) A process for producing a tetrafluorobenzenecarbaldehyde represented by formula (3) 
(wherein m and n have the same meanings as defined in above (1)), comprising hydrolyzing a tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) 
(wherein m and n have the same meanings as defined above).
(8) A process for producing a tetrafluorobenzenecarbaldehyde described in above (6) using fluorobenzenecarbaldehyde dialkylacetal represented by formula (2) 
obtained by catalytically reducing a tetrafluorocyanobenzene represented by formula (1) 
(wherein m and n have the same meanings as defined in above (1)) in the presence of an alkyl alcohol represented by Rxe2x80x94OH (wherein R has the same meanings as defined in above (1)) and an acid.
(9) The process for producing a tetrafluorobenzenecarbaldehyde as described in above (7) or (8), wherein water is added and then the hydrolysis is performed while separating an alkyl alcohol by distillation.
(10) The process for producing a tetrafluorobenzenecarbaldehyde as described in any of above (7) to (9), wherein water in excess amount of 10 times in mol or more is used based on the acetal group of tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2).
(11) The process for producing a tetrafluorobenzenecarbaldehyde as described in any one of (7) to (9), wherein the tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) is 2,3,5,6-tetrafluorobenzaldehyde dialkylacetal or 2,3,5,6-tetrafluoroterephthalaldehyde dialkylacetal, and the tetrafluorobenzenecarbaldehyde represented by formula (3) is corresponding 2,3,5,6-tetrafluorobenzaldehyde or 2,3,5,6-tetrafluoroterephthalaldehyde.
(12) A process for producing a tetrafluorobenzenemethanol represented by formula (4), 
(wherein m and n have the same meanings as defined above) comprising reducing a tetrafluorobenzenecarbaldehyde represented by formula (3) 
(wherein m and n have the same meanings as defined above), prepared by hydrolyzing a tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) 
(wherein m and n have the same meanings as defined above).
(13) The process for producing a tetrafluorobenzenemethanol as described in above (12), wherein the tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) is 2,3,5,6-tetrafluorobenzaldehyde dialkylacetal or 2,3,5,6-tetrafluoroterephthalaldehyde dialkylacetal, the tetrafluorobenzenecarbaldehyde represented by formula (3) is corresponding 2,3,5,6-tetrafluorobenzaldehyde or 2,3,5,6-tetrafluoroterephthalaldehyde, and the tetrafluorobenzenemethanol represented by formula (4) is corresponding 2,3,5,6-tetrafluorobenzyl alcohol or 2,3,5,6-tetrafluorobenzenedimethanol.
(14) Tetrafluorobenzenecarbaldehyde dimethylacetals represented by formula (5) 
(wherein m and n have the same meanings as defined in above (1)).
The present invention is described in detail below. A series of reactions in the present invention is shown in reaction formula below. 
In the reaction formula, R represents an alkyl group having from 1 to 4 carbon atoms and m represents 1 or 2, n represents 0 or 1, and m+n=2.
In the present invention, a tetrafluorocyanobenzene represented by formula (1) is used as a reaction starting material and the catalytic reduction reaction is performed in the presence of a specific alkyl alcohol and an acid in step (a), whereby a tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) is produced. Subsequently, in step (b), water is added to perform the hydrolysis, as a result, a tetrafluorobenzenecarbaldehyde represented by formula (3) can be produced. Next, by using highly pure tetrafluorobenzenecarbaldehyde obtained from step (b) or its aldehyde as material, tetrafluorobenzenemethanols can be produced in a high yield by an industrially useful method in step (c) without using a large amount of an expensive hydrogenated metal reagent.
As prior art related to the reaction used in the steps of the present invention, a method of hydrogenating pentafluorobenzonitrile using sponge nickel in the presence of a sulfuric acid and an alcohol to produce a pentafluorobenzaldehyde dialkylacetal, is disclosed in JP-A-63-39832 which comprises a reaction similar to the one in step (a) for converting a nitrile group into an acetal group.
As an example of the reaction for converting an acetal group into an aldehyde group in step (b), it is reported that 2,3,5,6-tetrafluorobenzaldehyde could be obtained by the hydrolysis of 2,3,5,6-tetrafluorobenzaldehyde diethylacetal synthesized starting from pentafluorobenzonitrile through a reaction with LiAlH4, though the yield is as low as 34% (see, J. General Chem. USSR, Vol. 39, No. 7, page 1576 (1969)).
The tetrafluorobenzenecarbaldehyde dialkylacetals represented by formula (2) can be produced according to step (a) of the present invention. Preferred examples include tetrafluorobenzaldehyde dimethylacetal and tetrafluoroterephthalaldehyde dimethylacetal.
As analogous compounds of the compound obtained by step (a), pentafluorobenzaldehyde dialkylacetal (see, JP-A-63-39832) and tetrafluorobenzaldehyde diethylacetal (see, J. General Chem. USSR, Vol. 39, No. 7, page 1576 (1969)) are known. However, no report is known on the tetrafluorobenzaldehyde dimethylacetal. Tetrafluorobenzaldehyde dimethylacetal is a novel and industrially very useful compound.
Specific examples of the tetrafluorocyanobenzene represented by formula (1) used as the starting material in the present invention include 2,3,5,6-tetrafluorobenzonitrile, 2,3,4,5-tetrafluorobenzonitrile, 2,3,4,6-tetrafluorobenzonitrile, 2,3,5,6-tetrafluoroterephthalonitrile, 2,3,4,5-tetrafluorophthalonitrile and 2,3,4,6-tetrafluoroisophthalonitrile.
Among these, 2,3,5,6-tetrafluorobenzonitrile and 2,3,5,6-tetrafluoroterephthlonitrile are preferred.
Of these compounds, tetrafluorodicyanobenzenes can be produced, for example, by replacing the chlorine atom of a tetrachlorodicyanobenzene obtained as a result of chlorination of a dicyanobenzene, with fluorine of an alkaline fluoride. Specifically, JP-B-44-28493 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) discloses a method of reacting 2,3,5,6-tetrachloroterephthalonitrile with potassium fluoride to produce 2,3,5,6-tetrafluoroterephthalonitrile. The tetrafluorobenzonitrile can be produced by a method disclosed, for example, in International Patent Publication No. 9808795, a method of hydrogenolizing a fluorinated dicyanobenzene and thereby hydrodecyanating the cyano group only on one side.
Use of tetrafluorobenzonitrile obtained by the process of the present invention is advantageous particularly in the production of 2,3,5,6-tetrafluorobenzaldehyde dialkylacetal. The reason is that 2,3,5,6-tetrafluorobenzyl alcohol produced starting from this acetal is completely free of pentafluorobenzyl alcohol which may work out to a starting material of pyrethroids highly toxic to mammals.
As the catalyst used in the catalytic reduction in step (a), a metal catalyst such as nickel, palladium, platinum, ruthenium, cobalt or copper, may be used. Among these, a nickel catalyst is preferred. The catalyst may be a metal as it is or in the form of a supported catalyst. As the supporter, activated carbon, silica, alumina or the like may be used. Specific examples of preferred catalysts include sponge nickel catalyst. The amount of the catalyst added is not particularly limited, however, the catalyst is preferably used in an amount of 1 mass % or more based on the tetrafluorocyanobenzene represented by formula (1).
Also, it is effective to add a dissimilar metal component to the catalyst. To this purpose, copper, tin, chromium, lead, cadmium, antimony, bismuth, molybdenum, zinc, iron or the like may be added as an element or as salt thereof and among these, copper, lead, or zinc component is preferred. The amount of the dissimilar metal added to the catalyst is preferably 0.1 to 50 mass % based on the catalyst.
Examples of the acid for use in reaction in step (a) include sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, monochloroacetic acid, dichloroacetic acid and trifluoroacetic acid. Among these, sulfuric acid, hydrochloric acid and phosphoric acid are preferred.
The amount of the acid used is not particularly limited, however, the acid is preferably used in an amount of 1 times in mol or more based on the tetrafluorocyanobenzene represented by formula (1).
The alkyl alcohol represented by Rxe2x80x94OH wherein R represents an alkyl group having from 1 to 4 carbon atoms in the present invention includes an alkyl alcohol having from 1 to 4 carbon atoms. Specific examples thereof include methanol, ethanol, 2-propanol and n-butanol. Among these, methanol is most preferred.
Alcohol is preferably used 2 times in mol or more, more preferably 10 times in mol or more, based on the tetrafluorocyanobenzene represented by formula (1).
In step (a), a solvent is not indispensable, however, a solvent such as hydrocarbon (e.g., toluene, ethyl benzene), an ether (e.g., 1,4-dioxane, tetrahydrofuran), dimethyl folmamide (DMF), dimethyl sulfoticido (DMSO) or sulfolane, may also be used.
The reaction temperature is not particularly limited. However, the reaction is preferably performed at a temperature of from 0xc2x0 C. to around 100xc2x0 C.
The method for supplying hydrogen is not particularly limited and the hydrogen may be blown into the reaction solution or may be passed through or intermittently supplied to the vapor phase moiety. The hydrogen may also be supplied as a mixed gas together with an inert gas such as nitrogen. The hydrogen partial pressure may be from reduced pressure to applied pressure.
If water is present in the reaction of step (a), it is usually undesirable because the tetrafluorobenzenecarbaldehyde dialkylacetal is disadvantageously converted into tetrafluorobenzenecarbaldehyde or the like due to hydrolysis. However, small amount of water does not matter which exists in sponge nickel prepared as water suspension. It was proved that the water does not adverse the reaction result of reaction in step (a) as long as the amount of water is as small as 1 times in mol or less based on the acetal group.
It is effective to perform a heat treatment after the tetrafluorocyanobenzene represented by formula (1) as a starting material is consumed in reaction of step (a). The heat treatment enables to increase the yield of the tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2). The heat treatment is preferably performed at a temperature of from 40xc2x0 C. to around 100xc2x0 C. for 0.1 hour to 24 hours.
In the present invention, the tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) obtained by step (a) may be purified by distillation, extraction, two-layer separation or the like, or may be used in the subsequent hydrolysis reaction of reaction step (b) without passing through any particular purification. Or the tetrafluorobenzenecarbaldehyde dialkylacetal may be used as a mixture with tetrafluorobenzenecarbaldehyde represented by formula (3).
The end point of reaction in step (a) may be set at the point when hydrogen corresponding to 1 mol based on the cyano group of tetrafluorocyanobenzene is consumed or may be determined by measuring the amount of starting material consumed using an analysis instrument such as gas chromatography or by performing quantitative analysis of the amount of tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) or tetrafluorobenzenecarbaldehyde represented by formula (3) produced. Here, according to the process of the present invention, it is confirmed that in reaction of step (a), the yield does not decrease due to the decomposition or the like of product even if the reaction time is excessively prolonged.
The tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) obtained by step (a) is hydrolyzed according to step (b) and thereby converted into tetrafluorobenzenecarbaldehyde represented by formula (3).
In the acetalization shown in step (a), tetrafluorobenzenecarbaldehyde monoalkylacetal is produced in some cases but is similarly converted into tetrafluorobenzenecarbaldehyde by the hydrolysis.
The reaction in step (b) may be performed in the presence of an acid. The acid used in this reaction is sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, monochloroacetic acid, dichloroacetic acid or trifluoroacetic acid, preferably sulfuric acid, hydrochloric acid or phosphoric acid. The amount of acid to be used is not particular limited. In step (b), a method of continuously using the acid used in step (a) is preferably used.
The amount of water added in step (b) is not particularly limited as long as it is 1 time in mol or more based on the acetal group of tetrafluorobenzenecarbaldehyde alkylacetal represented by formula (2) produced. However, since the reaction in step (b) is an equilibrium reaction, excess water of 10 times in mol or more is preferably used, so that the tetrafluorobenzenecarbaldehyde represented by formula (3) can be efficiently obtained in a high yield and a high purity.
In step (b), a solvent is not essential, however, a solvent such as hydrocarbon (e.g., toluene, ethylbenzene), an ether (e.g., 1,4-dioxane, tetrahydrofuran), DMF, DMSO or sulfolane may also be used.
The reaction temperature is not particularly limited but the reaction is preferably performed at a temperature of from 0xc2x0 C. to around 200xc2x0 C.
In step (b), when the alcohol contained and the alcohol produced by the reaction are removed by distillation, the equilibrium is shifted to the production side. By this so-called reactive distillation, the tetrafluorobenzenecarbaldehyde dialkylacetal represented by formula (2) contained can be efficiently converted into tetrafluorobenzenecarbaldehyde represented by formula (3). By this reactive distillation, the equilibrium is effectively shifted to the production side, so that the amounts of acid and water used in the hydrolysis reaction in step (b) can be greatly reduced.
In performing the reactive distillation, methanol is most preferably used as the alcohol. Methanol is inexpensive and has a low boiling point (64.7xc2x0 C.), therefore, it can be easily distilled off and the hydrolysis reaction in step (b) can be efficiently accelerated. Furthermore, methanol does not form an azeotropic mixture with water and therefore, water can be prevented from distilling, so that the reaction of step (b) can be accelerated and at the same time, the recycle use of alcohol can be facilitated.
The tetrafluorobenzenecarbaldehyde represented by formula (3) obtained by step (b) can be purified by distillation, extraction, two-layer separation or the like. Among these, distillation is the most suitable method, in which a high purity tetrafluorobenzenecarbaldehyde can be obtained.
The tetrafluorobenzenecarbaldehyde is distilled out as a two-layer fraction with water. By separating the fraction into two layers, high-purity tetrafluorobenzenecarbaldehyde can be obtained. The tetrafluorobenzenecarbaldehyde dissolved in the aqueous layer can be recovered by the extraction using an organic solvent. The extraction solvent is not particularly limited but an aromatic hydrocarbon such as toluene is preferably used. The aqueous layer obtained may also be recycled as the water added in the hydrolysis in step (b) without extracting the tetrafluorobenzenecarbaldehyde in the aqueous layer. By this recycle use, not only the yield of tetrafluorobenzenecarbaldehyde is increased but also the amount of waste water treated can be greatly reduced.
By reducing the tetrafluorobenzenecarbaldehyde produced in step (b) represented by formula (3) according to step (c), a tetrafluorobenzenemethanol represented by formula (4) can be produced.
In the reaction of step (c), a metal catalyst such as nickel, palladium, platinum, ruthenium, cobalt, copper or the like is used. Among these, a nickel catalyst is preferred. It is also effective to add a dissimilar metal to the catalyst and to this effect, copper, tin, chromium, lead, cadmium, antimony, bismuth, zinc, iron or the like is added. The catalyst may be a metal as it is or in the form of a supported catalyst. As the supporter, activated carbon, silica, alumina or the like may be used. Specific examples of preferred catalysts include sponge nickel catalyst. A method of reducing aldehyde into an alcohol using a metal hydride such as NaBH4 or LiAlH4 may also be used.
A solvent is not essential in the reaction of step (c), however, a hydrocarbon such as toluene and ethyl benzene, an alcohol such as methanol, ethanol and 2-propanol, an ether such as 1,4-dioxane and tetrahydrofuran, or a carboxylic acid such as acetic acid and formic acid may be used as a solvent. Among these, an aromatic hydrocarbon such as toluene and ethyl benzene is preferred.
The reaction form is not particularly limited, however, a catalyst suspension flowing system, a fixed bed flowing system, a trickle bed or a batch system may be used.
The reaction temperature is not particularly limited, however, the reaction is preferably performed at a temperature of from ordinary temperature to around 200xc2x0 C. With respect to the reaction pressure, the reaction may be performed under a pressure of from atmospheric pressure to applied pressure. The hydrogen partial pressure in the hydrogen reduction is not particularly limited but it is preferably 1 MPa or less.
The tetrafluorobenzenemethanol represented by formula (4) obtained by step (c) may be purified by distillation, extraction or two-layer separation after the catalyst is separated by an operation such as filtration, centrifugation or precipitation.